When a display device, such as a liquid crystal display device, is used under a bright environment, for example when such a display device is used under an environment where daylight enters, such external light reflects off the screen of the display device, reducing visibility. As the system for preventing such a reduction in visibility, there is a system for controlling the luminance of a backlight in a transmissive display device (for example, see Patent Document 1).
Further, in order to improve the luminance of a color display device, there is a technique where a single pixel is not constituted by three sub-pixels in R (red), G (green) and B (blue) but is constituted by four sub-pixels in R, G, B and W (white) (for example, see Patent Document 2). In a display device where a single pixel is constituted by four sub-pixels in R, G, B and W, the luminance of display is improved regardless of a surrounding environment, resulting in preventing a reduction in visibility when the display device is used under a bright environment.
As the liquid crystal display device for displaying video images, there is a display device which is configured to supply the display panel with signals based on image data at a frame frequency twice the frame frequency of input image data (such as 60 Hz) (for example, see Patent Document 3). In such a display device, a certain frame is inserted in between respective frames of input image data. Such an inserted frame is, for example, an entirely black image frame where a black image is displayed on the entire screen (black image frame). Although image blur is observed in some cases when the respective original black image frames are successively displayed in a liquid crystal display device, it is possible to insert a black image frame every single frame in order to reduce the probability of such image blur being observed. For the purpose of preventing the luminance of observed video images from lowering, a gray image frame, an entirely monochrome image where a white image is displayed on the entire screen (white image frame) or an image frame, which is generated based on original images therebefore and thereafter by interpolating processing, is employed in some cases, in place of a black image frame. Hereinbelow, a case where a display panel is driven by being supplied signals at a frame frequency twice the frame frequency of input image data is referred to double-speed drive. The gray image frame may contain a black image frame and a white image frame unless otherwise specified.